What is macroecology?
How do we do it?
Large observational data
Some theory, but not much currently
Makes it tough to get at mechanism
…but maybe that’s not the point
What do parasites have to do with macroecology?
- Parasites can provide good tests of macroecological ideas
An example:
- Some macreocological ideas claim that metabolic constraints on thermoregulation determine the distribution of diversity. Ectotherms (like parasites) could provide a good test of this specific hypothesis
I pitched this in 2011!!
What’s the scope of parasite macroecology we’ll cover
the standard flavors (ldr, range size stuff, parasite body size scaling, etc. )
host-parasite networks ( the next frontier!)
first we need some data
London Natural History Museum Host-Helminth data
299 geopolitical locations
23601 parasite species
14933 host species
94561 interactions
London Natural History Museum Host-Helminth data
others exist, like VIRION, GMPD2.0, etc.
Recall this figure of parasite taxonomic diversity?
Latitudinal diversity gradient
tendency for species richness to be highest near the equator and lowest near the poles
Think-pair share (3 minutes): How many of the putative mechanisms underlying this pattern can we come up?
Latitudinal diversity gradient
Latitudinal diversity gradient (but with parasites)
Another potential mechanism
The mid-domain effect
Interesting because it is essentially a null model
Ignores all species differences and generates the relationship
Bergmann’s rule
tendency for species body size to be larger away from equator
Main proposed mechanism is larger body mass increases surface-to-volume ratio, important for heat retention.
Do we expect parasites to follow Bergmann’s rule?
Can be examined across species or within a single species!
Bergmann’s rule
Bergmann’s rule
Is this support?
What’s going on with temperature in the right panels?
Harrison’s rule
Large parasites should only infect large host species
This is a modified Harrison’s rule from Poulin (how?)
Island biogeography theory
Island biogeography theory (but with parasites)
Island biogeography theory (but with parasites)
Distance decay relationships
Island biogeography is supposed to give us equilibrial species richness
But macroecology can also relate to species composition
Increasing geographic distance should result in more dissimilar communities
Distance decay relationships
What if all these patterns are just driven by host richness?
Totally possible. Parasites are simply tracking their hosts, and their showing macroecological patterns is simply a function of the host community
Ways around this
standardize parasite diversity by host diversity
compare strength of macroecological relationships between host and parasite communities
give up (jk)
Parasite macroecology special issue
Check out this special issue for some neat parasite macroecology
The macroecology of species interaction networks
We’ve seen networks before
The macroecology of species interaction networks
We’ve seen networks before
The macroecology of species interaction networks
We’ve seen networks before
The macroecology of species interaction networks
We’ve seen networks before
The macroecology of species interaction networks
That’s because networks are awesome!
End of lecture 1
What have we learned
There are many ways to study host-parasite interactions
Macroecology is one way, which looks at large spatial/taxonomic/temporal patterns
Ignores a lot of detail and specifics of host-parasite interactions
But is still neato
Now let’s talk about networks
Why networks?
They are also neato
They relate to concepts we’ve already covered (specificity, host range, parasite species richness, etc. etc.)
Host-parasite interactions do not exist in isolation (we saw that!)
Unipartite networks
consist of one class of interactor and the links between them
- transportation networks
- social networks
- sexual contact networks
- etc.
Bipartite networks
consist of two classes of interactors
- actor-movie
- artist-listener
- plant-pollinator
- host-parasite
The web of interactions between small mammals and their parasites in New Mexico
What can we measure about these networks?
Centrality
degree : sum of links for a given interactor
closeness : weighted distance between interactors
betweenness : weighted by shortest paths that pass through an interactor
What does each of these correspond to in a host-parasite network? (5 minute paired discussion)
What can we measure about these networks?
- Nestedness : tendency of interactions to form into nested subsets
Have we seen concepts like this before? What does this start to get at?
The macroecology of host-parasite networks
A lot of this is beyond the course, so we won’t really cover it.
The core goal is to leverage macroecological ideas into thinking about how host-parasite networks change across spatial and environmental gradients
And folks have been thinking about this!
But what if we simplify our approach to just considering social networks (unipartite)?
Disease spread in networked populations
We saw this in the sexual contact network lecture!
But we didn’t talk about mitigation
Who would you vaccinate in this network?
Removing a single well-connected individual
Removing the top interactors (compared to random, based on degree)
Removing the top interactors (compared to random, based on closeness)
That was fun, right!?
The structure of the network really matters when considering control options
This is why targeted vaccination campaigns work!
We don’t ‘ring cull’ people, right?
But what if we simplify our approach to just considering spatial networks?
We can think about disease transmission in these networks
parasites in metapopulations + hall and becker work
- other bits? spectralSpread bits? https://onlinelibrary.wiley.com/doi/full/10.1111/eva.12294